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Positive energy balance is associated with accelerated muscle atrophy and increased erythrocyte glutathione turnover during 5 wk of bed rest^1,2,3

Gianni Biolo, Francesco Agostini, Bostjan Simunic, Mariella Sturma, Lucio Torelli, Jean Charles Preiser, Ginette Deby-Dupont, Paolo Magni, Felice Strollo, Pietro di Prampero, Gianfranco Guarnieri, Igor B Mekjavic, Rado Piot and Marco V Narici

¹ From the Department of Clinical, Morphological and Technological Sciences, Division of Internal Medicine, and the Department of Mathematics and Informatics (LT), University of Trieste, Trieste, Italy (GB, FA, MS, and GG); the Institute for Kinesiology Research, University of Primorska, Koper, Slovenia (BS and RP); the Centre for Oxygen, Research and Development, University of Liege, Liege, Belgium (JCP and GD-D); the Division of Endocrinology, University of Milan, Milan, Italy (PM); the Division of Endocrinology and Metabolism, INRCA, Rome, Italy (FS); the Section of Physiology, Department of Biomedical Sciences and Microgravity, Ageing, Training, and Immobility (MATI), University of Udine, Udine, Italy (PdP); the Department of Automation, Biocybernetics and Robotics, Institute Jozef Stefan, Ljubljana, Slovenia (IBM); and the Institute for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Manchester, United Kingdom (MVN). RP and MVN contributed equally to the study and the manuscript

Background: Physical inactivity is often associated with positive energy balance and fat gain.

Objective: We aimed to assess whether energy intake in excess of requirement activates systemic inflammation and antioxidant defenses and accelerates muscle atrophy induced by inactivity.

Design: Nineteen healthy male volunteers were studied before and at the end of 5 wk of bed rest. Subjects were allowed to spontaneously adapt to decreased energy requirement (study A, n = 10) or were provided with an activity-matched diet (study B, n = 9). Groups with higher (HEB) or lower (LEB) energy balance were identified according to median values of inactivity-induced changes in fat mass (FM, assessed by bioelectrical impedance analysis).

Results: In pooled subjects (n = 19; median FM: 1.4 kg), bed rest–mediated decreases in fat-free mass (bioelectrical impedance analysis) and vastus lateralis thickness (ultrasound imaging) were significantly greater (P < 0.03) in HEB_AB (–3.8 ± 0.4 kg and –0.32 ± 0.04 cm, respectively) than in LEB_AB (–2.3 ± 0.5 kg and –0.09 ± 0.04 cm, respectively) subjects. In study A (median FM: 1.8 kg), bed rest–mediated increases in plasma leptin, C-reactive protein, and myeloperoxidase were greater (P < 0.04) in HEB_A than in LEB_A subjects. Bed rest–mediated changes of glutathione synthesis rate in eythrocytes (L-[3,3-²H₂]cysteine incorporation) were greater (P = 0.03) in HEB_A (from 70 ± 19 to 164 ± 29%/d) than in LEB_A (from 103 ± 23 to 84 ± 27%/d) subjects.

Conclusions: Positive energy balance during inactivity is associated with greater muscle atrophy and with activation of systemic inflammation and of antioxidant defenses. Optimizing caloric intake may be a useful strategy for mitigating muscle loss during period of chronic inactivity.